This is in relation to improvements in transducers, and more particularly to a transducer which has a diaphragm with an expanse extending generally in a plane and mounted in such a fashion that this expanse is movable in the direction of the plane. Coil means are attached to this expanse. Magnetic field means for producing a magnetic field adjacent to the coil means complete the transducer.
Various types of audio transducers, as exemplified by audio loudspeakers, are known in the prior art. One common form of transducer comprises a cone, with an electromagnetic motor driving element, mounted on a frame through a flexible expanse which bounds the perimeter of the cone. Generally speaking, such a transducer is characterized by relatively high diaphragm and coil mass which results in high inertial forces in the diaphragm and reduces its frequency response at high frequencies; or, the diaphragm and coil may be of relatively low mass and have reduced low frequency reproducing ability. Typically, the diaphragm is molded from a paper type of product which renders it susceptible to changes in relative humidiity. This alters frequency response and limits the life of the transducer.
Another type of loudspeaker known in the art comprises a horn type speaker having a flat diaphragm element which oscillates normal to the plane of the diaphragm element in response to activation by an electromagnetic driving element. The central diaphragm element is again mounted on a frame by means of an annular portion bounding the central expanse described. In some instances, such may be suspended and directly attached to a voice coil. With this type of speaker a rather large horn is required properly to direct and focus the sound waves produced. Again, by reason of the mass of the diaphragm and voice coil, the frequency response of the transducer tends to drop off at high frequencies. The transducers just described furthermore tend to be very expensive.
Audio transducers have characteristically become more complicated in design, the manufacturers relying on sealed cabinets, extremely heavy machine parts, and complicated voice coil arrangements in order to achieve the ultimate transducer.
Prior art speakers generally have exhibited a sudden drop in frequency response at the high end of the audio spectrum, typically above 20K hertz. This sudden decrease in frequency response has generally been attributed to high inertial coils and diaphragms, which are incapable of vibrating at extremely high frequencies.
Additionally, since an audio transducer which is responsive to low frequencies, in the vicinity of 20 to 250 hertz, is generally not responsive to frequencies above 15K hertz, several types or sizes of transducers are incorporated into a single cabinet, in order to provide adequate frequency response over the entire audio spectrum. The use of multiple transducers requires the incorporation of complex crossover networks to isolate audio signals traveling to or emanating from the individual transducers.
Generally, an object of this invention is to provide an improved transducer featuring a construction which overcomes difficulties and shortcomings of the type I have indicated.
More specifically, an object of the invention is to provide a transducer with a novel diaphragm construction wherein the diaphragm is of relatively low mass, the diaphragm also being ultimately flexible to provide essentially linear frequency response over the audio spectrum.
A feature of the transducer of the invention is a construction of the diaphragm which enables the manufacture of the diaphragm from material other than pressed material such as paper. As specifically comtemplated, the diaphragm may be manufactured, for instance, from a Mylar type of material. Such and similar material are moisture resistent and produce, over extended periods of time, a consistent predictable response to oscillation induced by an electromagnetic driving element.
The further object and feature of the invention is the provision of a transducer which may be simply manufactured without extreme criticality required in placement of parts and mountings, etc. Materials involved in construction of the transducer are readily available. All of the above tend to result in economies of manufacture.
Another feature and advantage of a transducer contemplated is derived from the flexibility of the diaphragm. This flexibility enables the diaphragm to expend its energy in making sound waves with minimal transmission of energy to the frame mounting the diaphragm and subsequent reduction in speaker efficiency.
A further object of the instant invention is to provide an audio transducer which exhibits a linearly decreasing frequency response at frequencies above 20K hertz by virtue of having a low inertia coil and diaphragm.
Another object of the instant invention is to provide an audio transducer which does not require a complex crossover network to accurately reproduce sound over the full audio spectrum.
The transducer of this instant application includes a generally rectangular open frame which carries opposing permanent magnets which generate what is referred to herein as opposing magnetic fields. A flexible diaphragm is secured to the frame and passes through the magnetic field. An elongate looped coil is carried on the diaphragm adjacent the opposed magnetic fields. A signal of variable amplitude in the coil accompanies movement of the diaphragm in what is described as rolling, linear movement.
These and other objects and advantages of the instant invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings.